a. Field of the Invention
The present disclosure relates generally to medical devices having force-sensing capabilities. More particularly, the instant disclosure relates to force-sensing catheters.
b. Background Art
Electrophysiology catheters are used in a variety of diagnostic, therapeutic, and/or mapping and ablative procedures to diagnose and/or correct conditions such as atrial arrhythmias, including, for example, ectopic atrial tachycardia, atrial fibrillation, and atrial flutter. Arrhythmias can create a variety of conditions including irregular heart rates, loss of synchronous atrioventricular contractions and stasis of blood flow in a chamber of a heart which can lead to a variety of symptomatic and asymptomatic ailments and even death.
Typically, a catheter is deployed into vasculature of a patient via a percutaneous approach, such as through a femoral or subclavian artery. The catheter is advanced through the vasculature to an intended site, for example, a site within the heart of the patient. The catheter may carry one or more electrodes that can be used for cardiac mapping or diagnosis, ablation and/or other therapy delivery modes, or both, for example. Once at the intended site, treatment can include, for example, radio frequency (RF) ablation, cryoablation, laser ablation, chemical ablation, high-intensity focused ultrasound-based ablation, microwave ablation, and/or other ablation treatments. The catheter imparts ablative energy to cardiac tissue to create one or more lesions in the cardiac tissue. This lesion disrupts undesirable cardiac activation pathways and thereby limits, corrals, or prevents errant conduction signals that can form the basis for arrhythmias.
In order to advance a distal tip of the catheter through the vasculature, a clinician may manipulate a proximal end of the catheter by sequentially or simultaneously applying torque, and longitudinal or axil pushing force. The distal tip of the catheter may also be selectively deflected or rotated in a desired direction if the catheter is steerable from the proximal end. It can be difficult to manipulate catheters in this manner, and it can be important to have a reliable indication of the force being applied to the cardiac tissue via this manipulation of the catheter. During an ablative procedure, the amount of pressure being applied to the tissue can influence the outcome of the procedure and/or the amount of time required to complete a procedure. Also, there may be some safety advantages to knowing how much pressure the catheter is applying to the cardiac tissue.
An exemplary known force-sensing catheter is described in U.S. patent application Ser. No. 13/547,397 to Meredith. Such a catheter includes a force-sensing tip having a spring aligned along the axis of the catheter that deflects under pressure. Movement of the spring is determined by following movement of tracker coils within the catheter tip, before and after deflection of the mechanical spring, using a magnetic resonance imaging (MRI) system. The distance traversed by the tracker coils is converted to the distance of compression of the mechanical spring, which is then used to determine the force applied to the catheter tip using the axial spring constant of the mechanical spring. Such a catheter, however, only measures axial force applied by the tip. Furthermore, the catheter requires an external imaging system to follow the location of the tracker coils in order to determine force.